This invention relates to reducing errors in digital communication.
When a bit stream is sent from a transmitter to a receiver through a channel, bit errors may occur. Typical international standards applied to a high quality, 20 km long channel allow only one severely errored second (SES) per month during which the bit-error ratio (BER) is higher than 10.sup.-3 (1 bit error per 1000 bits).
When the equipment in the channel breaks, all of the communicated bits may be lost for an extended period of time. Failures of this kind are often handled by providing duplicate hot standby equipment that can be switched into service after the failure has been detected. Such hot standby switching normally is associated with a short period of high bit errors.
Even in the absence of such major failures, communication channels by their nature typically cause occasional isolated errors or error bursts in the bit stream being carried. In radio relay systems multipath fading can be a frequent source of such errors. Complex error detection and correction schemes are often used on a digital channel to detect and correct these occasional errors.